CAD programs are used today in connection with a plurality of tasks in the fields of construction, design and development. Present-day CAD programs provide, besides the original functionality of technical drawing, tools for the whole development process and sometimes also for further fields like, for example, manufacturing and quality control. The term “CAD program” in the sense used herein is therefore to be understood in its broadest meaning as any computer program that comprises a drawing and/or design module and possibly further modules. A widely used CAD program is manufactured and sold by the assignee under the trademark “AutoCAD”.
It is general practice when using such a CAD program in the design process to create a 3D model of the intended apparatus or the intended assembly. This 3D model may be viewed from all perspectives in a high, sometimes even photo-realistic quality. However, production plans that represent exact 2D views of the 3D model are required, at the latest, in the preparation steps of the production process. In particular, the usual normal projections (front view, side views, top view, bottom view, rear view) as well as further views are required. The term “view” in this context comprises both sectional and non-sectional views.
It is known to calculate such 2D views from the 3D model by mathematical projection methods. These methods substantially correspond to methods that are already implemented in most CAD programs since they are also used for generating a view of the 3D model that is displayed on the computer monitor.
Such a calculated 2D projection, however, is usually less than optimal. This is because there are, in particular for often-used standard parts or standard features of a part, conventions for the “correct” two-dimensional representation that deviate from the mathematically calculated projection. Such a deviation may possibly be acceptable for the mere visualization of a 3D model. However, a representation conforming to the applicable standards is necessary for an exact 2D view that is to be used, for example, as a production plan.
An example for the facts mentioned just above is shown in FIG. 1a and FIG. 1b. FIG. 1a represents, as a 2D view 10, the standard-conforming sectional view of a screw connection of two parts 12, 14 by means of a screw 16 and a nut 18. The middle axis of the screw 16 is located in the sectioning plane. It is shown in FIG. 1b, as an example, how a 2D view 10 of the same assembly is calculated as a 2D projection by known CAD programs.
Although the representation of FIG. 1b is correct from a mathematical point of view, there are several undesirable deviations with respect to the standard-conforming view of FIG. 1a. First, the whole screw connection in FIG. 1b is marked as sectioned by a hatching. It would instead be the usual way to show the whole screw connection in a non-sectioned front view in spite of the sectioned representation of the parts 12 and 14. The second deviation is that in FIG. 1b neither the axis line 20 nor the thread lines 22 denoting the depth of the thread are shown. The third deviation is that FIG. 1b shows the hexagon socket 24 and the hexagon nut 18 in an unusual way. It would be the usual and thus preferable representation to show, as depicted in FIG. 1a, the nut 18 in a front view that is symmetrical with respect to the center axis. The same is true for the hexagon socket 24, for which furthermore dashed lines should be used in order to designate that the hexagon socket 24 is located inside the head cap of the screw 16.
The deviations of the calculated 2D projection from the standard-conforming (or at least common) representation, which have been exemplified here, require a substantial amount of finishing operations. So, for example, the axis line 20 and the thread lines 22 must be inserted by manual drawing operations. The user has to turn the screw connection in the 3D model in an appropriate way in order to obtain a symmetric arrangement of the nut 18 and the hexagon socket 24. Furthermore, several finishing steps are necessary with respect to the sectional hatchings. These operations require much effort and are error-prone. They divert the attention of the user from the actual design tasks towards subordinate, formal aspects and thus diminish the benefits of CAD program.
The article “CAD für den Maschinenbau: Mit den BCT-Assistenten auf dem richtigen Weg” in the journal “CAD-CAM Report”, No. 9, 1998, pages 30-36 discloses a CAD program in which parts with integrated assembly logic, e.g., for screw connections, may be stored and managed in a 3D pool. Logical links may be implemented for generating drawings such that, e.g., ball bearings will be shown automatically in a correct way, whereas screws will be shown in a non-sectioned way. Similar automatic methods may be used to suppress or cut out certain features in a 2D sectional representation.